1. Field of the Invention
The present invention relates to a process for recovering hydrocarbons from inert gas-hydrocarbon vapor mixtures, and more particularly, to an improved process for recovering vaporized gasoline, distillates, benzene, solvents and the like from a mixture thereof with inert gas.
2. Description of the Prior Art
In handling multi component and single component hydrocarbon liquids such as gasoline, inert gas hydrocarbon vapor mixtures are readily produced which cannot be vented directly to the atmosphere due to the resulting pollution and fire or explosion hazard. As a result, a variety of processes have heretofore been developed and used for removing hydrocarbon vapors from inert gas-hydrocarbon vapor mixtures whereby the remaining inert gas can be safely vented to the atmosphere. The removed hydrocarbon vapors are recovered, processed further or disposed of.
A particularly suitable prior art process for recovering hydrocarbons from air-hydrocarbon vapor mixtures and the like is described in U.S. Pat. No. 5,154,735 issued to Dinsmore et al. on Oct. 13, 1992. The process comprises the steps of flowing the inlet air-hydrocarbon vapor mixture through a first bed of solid adsorbent whereby hydrocarbons are adsorbed on the bed and a residue gas stream comprised of substantially hydrocarbon-free air which is vented to the atmosphere is produced. A second bed of solid adsorbent having hydrocarbons adsorbed thereon is regenerated by vacuum pumping whereby hydrocarbons are desorbed from the bed and a hydrocarbon rich air-hydrocarbon mixture is produced. A substantial portion of the hydrocarbons are recovered from the hydrocarbon rich air-hydrocarbon vapor mixture produced during the regeneration. The beds of adsorbent are periodically changed from adsorption to regeneration and vice versa so that the bed which has just become loaded with adsorbed hydrocarbons is regenerated, i.e., evacuated and stripped of hydrocarbons and the bed which has just been regenerated adsorbs hydrocarbons. The evacuation of the beds during regeneration is accomplished in the process of U.S. Pat. No. 5,154,735 by vacuum pumping with a liquid seal vacuum pump. In order to increase the evacuation, a positive displacement booster pump connected upstream and in series with the liquid seal vacuum pump is utilized in combination with the introduction of a relatively small quantity of hydrocarbon-free air into the bed being evacuated whereby additional hydrocarbons are stripped from the bed. The further. evacuation accomplished by the booster pump and air stripping results in the bed being regenerated to a low hydrocarbon content and in substantially hydrocarbon-free air being vented to the atmosphere.
While the above described process utilizing a positive displacement booster pump in series with a liquid seal vacuum pump has achieved great commercial success, the cost of the pumps, their maintenance and their operation are expensive. Thus, there are needs for improved processes capable of regenerating beds of solid adsorbent to a very low hydrocarbon content which are less costly to install, operate and maintain.
The present invention provides improved processes for recovering hydrocarbon vapors from intermittent or continuous inlet inert gas-hydrocarbon vapor mixtures which meet the needs described above and overcome the deficiencies of the prior art. The improved processes of the present invention are basically comprised of the following steps. An inlet inert gas-hydrocarbon vapor mixture is flowed through a first bed of solid adsorbent having an affinity for hydrocarbons whereby hydrocarbons are adsorbed on the bed and a residue gas stream comprised of substantially hydrocarbon-free inert gas is produced. The substantially hydrocarbon-free inert gas is vented to the atmosphere. A second bed of solid adsorbent having hydrocarbons adsorbed thereon is evacuated with a simple ejector which is operated by a continuous motive liquid stream whereby a major portion of the hydrocarbons are desorbed from the bed and an inert gas-hydrocarbon-rich vapor mixture commingled with motive liquid is produced. The inert gas-hydrocarbon-rich vapor mixture is separated from the motive liquid and is processed further or disposed of. The flow pattern of the inlet inert gas-hydrocarbon vapor mixture is periodically changed so that when the bed through which the inlet inert gas-hydrocarbon vapor mixture is flowing becomes loaded with adsorbed hydrocarbons, the inlet inert gas-hydrocarbon vapor mixture is caused to flow through the bed which has just been evacuated and the bed loaded with adsorbed hydrocarbons is regenerated. The basic processes also preferably include the step of introducing a quantity of hydrocarbon-free inert stripping gas into the bed being evacuated whereby additional hydrocarbons are stripped from the bed and additional inert gas-hydrocarbon-rich vapor mixture co-mingled with motive liquid is produced.
In alternate embodiments of the basic process of the present invention, the motive liquid can be recirculated through the ejector or the motive liquid can be a continuous stream which passes through the ejector only once. In addition, the motive liquid can be a liquid which has an affinity for the desorbed hydrocarbon vapor whereby a major portion of the hydrocarbon vapor is absorbed in the motive liquid as it passes through the ejector.
In addition to the above described basic processes, the present invention provides a variety of additional process steps which can be utilized in accordance with this invention to liquefy and recover the desorbed hydrocarbon vapor.
It is, therefore, a general object of the present invention to provide improved processes for recovering hydrocarbons from inert gas-hydrocarbon vapor mixtures.
Other and further objects, features and advantages of the present invention will be readily apparent to those skilled in the art upon a reading of the description of preferred embodiments which follows when taken in conjunction with the accompanying drawings.